1. Field of the Invention
The invention relates to a stent/graft deployment catheter handle. More particularly, the invention relates to a stent/graft deployment catheter handle, incorporating a ratchet-like actuation mechanism, capable of deploying a stent/graft accurately.
2. Description of the Prior Art
An abdominal aortic aneurysm (AAA) is a sac caused by an abnormal dilatation of the wall of the aorta as it passes through the abdomen. The aorta is the main artery of the body, supplying blood to all organs and parts of the body except the lungs. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen, and finally divides into the iliac arteries which supply blood to the pelvis and lower extremities.
The AAA ordinarily occurs in the portion of the aorta below the kidneys. When left untreated, the aneurysm will eventually cause the sac to rupture with ensuing fatal hemorrhaging in a very short time. The repair of abdominal aortic aneurysms has typically required major abdominal surgery in which the diseased and aneurysmal segment of the aorta is bridged with a prosthetic device, such as a synthetic graft.
As with all major surgeries, there are many disadvantages to the above mentioned surgical technique, the foremost of which is the high mortality and morbidity rate associated with surgical intervention of this magnitude. Other disadvantages of conventional surgical repair include the extensive recovery period associated with such surgery; difficulties in suturing the graft to the aorta; the unsuitability of the surgery for many patients, particularly older patients exhibiting comorbid conditions; and the problems associated with performing the surgical procedure on an emergency basis after the aneurysm has already ruptured.
In view of the above mentioned disadvantages of conventional surgical repair techniques, techniques have been developed for repairing AAAs by intraluminally delivering an aortic graft to the aneurysm site through the use of a catheter based delivery system, and securing the graft within the aorta using an expandable stent. Since the first documented clinical application of this technique was reported by Parodi et al. in the Annals of Vascular Surgery, Volume 5, pages 491-499 (1991), the technique has gained more widespread recognition and is being used more commonly. As vascular surgeons have become more experienced with this endovascular technique, however, certain problems have been encountered relating to deployment and accurate positioning of the aortic graft.
The catheter based delivery system generally comprises a sheath and a plunger slidingly disposed within said sheath. A compressed aortic stent/graft, which comprises a graft disposed about a stent, is disposed within the distal end (the end closer to the heart when inserted) of the sheath. Upon positioning of the catheter within the patient, the sheath is retracted relative to the plunger, thereby exposing the stent/graft and allowing it to self-expand or be mechanically expanded. If properly positioned, the proximal end of the deployed stent/graft should coincide with the position of the distal end of the plunger upon initial positioning of the catheter. Generally, the sheath is retracted relative to the plunger simply by manually pulling the sheath away from the patient while holding the plunger still. U.S. Pat. No. 5,702,418 discloses a sheath having a knob, on the outer surface of its proximal end, to facilitate the manual retraction of the sheath as described above. One major problem with such a manual deployment method is that while retracting the sheath the plunger may be inadvertently moved, upstream or downstream, thereby displacing the predetermined deployment site for the stent/graft. Since the ultimate position of the deployed stent/graft is determined by the position of the distal end of the plunger just before deployment, if the plunger is inadvertently moved, upstream or downstream, while retracting the sheath, the stent/graft may not be properly positioned, and therefore, may not properly bridge the aneurysm upon deployment. It is critical, therefore, that the plunger not be moved during deployment of the stent/graft, i.e. during retraction of the sheath.
Friction between the outer surface of the compressed stent/graft and the inner surface of the sheath often makes retraction of the sheath a bit difficult. This difficult retraction of the sheath leads to fidgeting of the plunger by the surgeon during deployment and amplifies the problem of maintaining the plunger still during deployment. U.S. Pat. Nos. 5,391,172 and 5,697,948 disclose stent delivery handles for providing relative motion between the sheath of a stent delivery catheter and an underlying catheter, i.e. a plunger. These handles basically comprise a tube to which the plunger is attached to and within which the sheath is slidingly disposed. Holding on to the handle, one can retract the sheath by pulling it towards the proximal end of the handle. Although these handles provide a better grip onto the plunger, they do not decrease the likelihood that the entire handle, and therefore the plunger, will be displaced while the sheath is being retracted.
Another hybrid of a handle, produced by MedTronics Corp. (Eden Prairie, Minn.), comprises a rack and pinion design. The sheath, having a plurality of ridges on its outer surface, is slidingly disposed within a lumen in a handle and serves as the rack. A pinion rotatably attached to the handle and extending into the lumen is capable of shifting the sheath, the rack, in one direction. The proximal end of the plunger is fixed in the handle. Upon positioning of the catheter in the patient, the pinion is rotated, thereby retracting the sheath, relative to the plunger, and deploying the stent/graft. Although this design reduces the likelihood that the plunger will be moved relative to the sheath it has a major drawback. A large pinion is required to achieve the necessary force to shift the sheath relative to the plunger and to ensure passage of the sheath through a potential obstruction in the vasculature of a patient. A large pinion is bulky, and therefore, difficult to handle. Another problem with a large pinion is that it must be rotated many revolutions to withdraw the sheath only a small distance.